Traditionally, the polyester repair markets have utilized well-defined processes in the area of damage repair. Unsaturated polyester resins are used in primer surfacers, body fillers, or putties to resurface and reshape damaged areas. For ease of understanding, the term “body fillers” will be used in the following description; however, it is to be understood that the term includes, primer surfacers, body fillers, and body putties.
Unsaturated polyester resins (UPR) have dominated the chemical backbone of body fillers since the late 1950's, and they have changed little over the past 50 years. Improvements have been made by using premium unsaturated polyester resins which have unique UV resistance and air dry qualities, making them ideal for premium grade fillers. However, the premium resins are expensive, and the resulting physical properties are less than ideal, especially in the area of impact strength and adhesion to metal substrates. In order to improve the physical properties, the premium resins have been blended with lower cost, more flexible, tougher unsaturated polyester resins. However, the trade-off for the improved properties is reduced sandability. The more “flexibility” is built into the filler by way of altering the resin composition, the worse the sanding becomes. A surfacing agent is frequently included in the filler composition to overcome this deficiency.